Name: _______________________
PATTERNS OF INHERITANCE
(20 points total)
DEFINITIONS - MATCHING
Each match is worth 0.5 points each. This section is worth 8 points in total.
Match the choices below with the definitions:
A. alleles B. autosomes C. dominant D. genotype E. heterozygous
F. homozygous XXXXXXXXXXG. phenotype XXXXXXXXXXH. recessive XXXXXXXXXXI. sex chromosomes
J. wild type K. incomplete dominance L. codominance M. epistasis
N. polygenic inheritance XXXXXXXXXXO. pedigree P. ca
iers
XXXXXXXXXXActual genetic makeup
XXXXXXXXXXChromosomes determining maleness/femaleness
XXXXXXXXXXSituation in which an individual has identical alleles for a particular trait
XXXXXXXXXXGenes not expressed unless they are present in homozygous condition
XXXXXXXXXXExpression of a genetic trait
XXXXXXXXXXsituation in which an individual has different alleles making up the genotype for a particular trait
XXXXXXXXXXGenes for the same trait that may have different expressions
XXXXXXXXXXChromosomes regulating most body characteristics
XXXXXXXXXXThe more potent gene allele; masks the expression of less potent allele
XXXXXXXXXXTwo dominant alleles affect the phenotype in two different ways
XXXXXXXXXXA chart that tracks the inheritance of certain traits
XXXXXXXXXXThe phenotype most often encountered in nature
XXXXXXXXXXA phenotype that results from the additive effect of two or more genes
XXXXXXXXXXThe phenotype of the offspring is somewhere in between the phenotypes of the parents
XXXXXXXXXXA heterozygote who shows a normal phenotype
XXXXXXXXXXA gene at one locus will change the phenotypic expression of a gene at another locus
SHORT – ANSWER SECTION
Each response is worth 0.5 points each. This section is worth 2 points in total.
1. Using the image given describe Mendel’s Law of Segregation.
1. Using the image given describe Mendel’s Law of Independent assortment.
1. A monohy
id cross is _________________________________________, and the
phenotypic ratio would be ____________________.
1. A dihy
id cross is ___________________________________________, and the
phenotypic ratio would be ____________________.
PUNNETT SQUARES
Each response is worth 1 point each. This section is worth 9 points in total.
COMPLETE DOMINANCE
Some inherited traits display complete dominance (like Tay-Sachs disease and polydactyly). Such traits are controlled by a single gene with two alleles. One allele is completely dominant over the other. The two problems below involve traits controlled by genes on autosomes (chromosomes other than sex chromosomes) that display complete dominance.
Case 1: Cystic Fi
osis
Will and Kirsten have a 3-year old son named Ian. Ian is small for his age although he eats well. He has been to a respiratory specialist due to repeated bouts of respiratory infections including a bout of pneumonia for which Ian was hospitalized. Will and Kirsten mention to the doctor that they have been puzzled by how salty Ian’s skin tastes when they kiss him. After an examination and some tests, the specialists reports that Ian has cystic fi
osis. He has inherited two copies of a mutant allele on chromosome 7 that results in an abnormal protein channel across the mem
anes of certain cells including those of the lungs and pancreas. Chloride ions are not properly moved in or out of cells, with the result that the mucus and other secretions of the affected cells are very thick and sticky. The thick mucus in the lungs leads to respiratory infections. The thick pancreatic secretions cannot reach the small intestine, leading to problems with digestion. Ian’s parents are told to keep Ian on a healthy diet with vitamin supplements and to clap him on the back and chest twice a day to loosen mucus in the lungs. They learn that medicines are available to help Ian, but that life expectancy is about 30 years, and that Ian will have chronic health problems that will greatly diminish his quality of life. Ian is Will and Kirsten’s first child. They were trying to conceive a second child when Ian was diagnosed with cystic fi
osis.
1. Neither Will nor Kirsten display any symptoms of cystic fi
osis. Is the allele responsible for this disease dominant or recessive?
2. What must Ian’s genotype be?
3. What are Will and Kirsten’s genotypes?
4. Before continuing with their plans to have a second child, Will and Kirsten want to know the probability of having a normal child who is not a ca
ier of cystic fi
osis, a normal child who is a ca
ier, and another child with cystic fi
osis. What is the probability they could have a child with cystic fi
osis? Solve a Punnett Square to estimate this probability. Show your work below.
Case 2: Polycystic Kidney Disease (dominant lethal allele)
Maria is 38 years old. She and her husband Joe have 4 children. Maria has been diagnosed with polycystic kidney disease. She learns that cysts developing in her kidneys have damaged them severely. The damage will continue until the kidneys stop functioning. Maria faces dialysis and will eventually need a kidney transplant. Maria is tested for the allele that causes the disease and learns that her form of the disease is caused by a dominant mutation on chromosome 16. Maria is heterozygous for the trait. Her husband is confirmed to be homozygous recessive. Maria’s children offer the best hope of a match for a future kidney donation but must be free of the harmful allele.
5. What is the probability of Maria and Joe’s children inheriting this dominant harmful allele? Solve a Punnett Square to estimate this probability. Show your work below.
INCOMPLETE DOMINANCE
There are some situations in which the two alleles of a gene produce a “blended” effect in a heterozygous individual. Because neither allele is dominant over the other, capital and lowercase letters cannot be used as symbols. One of denoting alleles showing incomplete dominance is to designate both with a capital letter with a superscript or apostrophe added to one – such as A and A’. For this example of gene “A” then, this case of incomplete dominance has 3 possible phenotypes, one each for the genotypes AA, AA’ and A’A’.
Case 1: Delta 32 and the AIDS virus
Stephen Crohn is a gay man whose partner was the 5th person in the U.S. to die from AIDS. In spite of his exposure to the virus, Crohn has never shown any signs of the disease. Dr. O’Brien of the National Institute of Health found that Crohn’s resistance is due to a mutation called delta 32. It results in the blocking of a mem
ane channel through which HIV enters white blood cells. Inheriting two copies of delta 32 (D’D’) provides exceptional/complete resistance to HIV. The heterozygous condition (DD’) delays the onset of AIDS after initial infection because there are half the number of mem
ane passageways as are present in a person who is homozygous normal which slows down the rate of viral replication. The heterozygous genotype (DD’) can therefore be described as giving modest/partial resistance. The DD genotype provides no resistance to AIDS. Both of Stephen Crohn’s parents were heterozygous for the delta 32 mutation. Stephen’s genotype became known after his unexpected resistance to HIV.
6. In the cross between Stephen’s parents, what would have been the probability for one child between them of having Stephen’s homozygous genotype?
Solve a Punnett Square to estimate this probability. Show your work below.
Case 2: Delta 32 and the Black Plague
Dr. O’Brien extended his findings about the delta 32 mutation by looking for the mutation in descendants of survivors of the black plague in Great Britain. Because the bacterium that causes plague also begins its attack on the body by entering white blood cells, O’Brien wondered if this deadly disease could have selected for individuals with the mutation. He tested people in a small town in England in which about half the population had never become ill when the plague struck the community in 1665. He found a much higher percentage of the townspeople had the delta 32 mutation than in the populations of other continents. If O’Brien is co
ect, this mutation provided protection from an epidemic that killed 1/3 of Europeans. The heterozygous condition would probably have delayed onset of symptoms.
William was a survivor of the plague in 1665 because he was homozygous for the delta 32 mutation (D’D’). He moved to a town in England that was unaffected by the plague and ma
ies Elizabeth who was homozygous normal (DD).
7. Based upon what is now known of William and Elizabeths’ genotypes, what is the probability they could have a child with the partial resistance phenotype? Solve a Punnett Square to estimate this probability. Show your work below.
MULTIPLE ALLELES and CODOMINANCE
Sometimes there are multiple possibilities for a particular gene. When there are more than 2 possible alleles, the dominance relationships of all the alleles must be determined. An example of a trait governed by multiple alleles is ABO blood type. There are 3 alleles for the gene that codes for a protein located on the surface of red blood cells: IA, IB, and i. IA and IB are co-dominant. IA codes for the A protein, while IB codes for the B protein. When both IA and IB are present, both proteins are made. Therefore, IA and IB are co-dominant. Both IA and IB are dominant over i which does not code for any mem
ane protein. Genotypes for human blood types are shown below.
Type A IAIA or IAi Type B IBIB or IBi
Type AB IAIB Type O ii
Problem 1: ABO Blood Types
8. Peter is heterozygous for Type A blood. He ma
ies Lynn who has type O blood. Based upon their known genotypes, what is the possibility they could have a child with Type A blood? Solve a Punnett Square to estimate this probability. Show your work below.
Problem 2: ABO Blood Types
9. Ha
y has Type AB blood. He ma
ies Sally,